Powerbox Skoda Octavia - Performance Chip

Hello!
"Could you please ask for a friend of mine if you can make sense of this!"
It's a Skoda Octavia 2.0 TDI with 140 horsepower.
He installed this power box, but no one knows what it actually does or which manufacturer it's from.
He wants to buy the car, and the previous owner doesn't even know where the part came from. He supposedly got it from a friend, and supposedly it's supposed to save fuel!
Of course, something like that always raises a certain amount of suspicion, because you don't want to buy a pig in a poke. However, the car is still very nice and drives well, so he would like to know what kind of power box it is and what it does. The previous owner drove 15,000 km with the box installed.
Thank you in advance for your input. Best regards!

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Quote:

In situations like that, a certain amount of suspicion naturally arises, because you don't want to buy a pig in a poke.

The distrust is justified. These boxes fundamentally only distort the input signals that the control unit needs for further processing.

"Proper tuning is essentially impossible because these devices cannot influence the maps stored in the engine control unit (ECU), and adjusting those maps is essential for achieving good results and durability."

I would remove that thing, and if needed, we can get something decent from our landlord.